How Does Classical Conditioning Work?
This is my friend Sutton, who volunteered for a completely harmless experiment in classical conditioning.

Let's start by poking him in the eye.

Oh! He didn't like that. Look at the way his eye is all twitchy and red.

Actually, maybe it's not so surprising that Sutton's upset. Prodding his vitreous humour caused him great pain—and primal responses like pain and hunger are excellent fodder for classical conditioning.
Let's poke Sutton in the eye again.

Look at his silly little face. He's getting quite angry, isn't he?

In the context of classical conditioning, all this gratuitous eye poking is called an unconditioned stimulus (UCS).
And Sutton flinching in response to pain is known as an unconditioned response (UCR).

Ok, enough messing around. Let's start the experiment.
Step 1. The Neutral Stimulus
Today we're going to classically condition Sutton. Soon, he'll react to a perfectly harmless object as if it's going to cause him great pain.
First we need our neutral stimulus (NS). This can be any specific trigger, like a sight or a sound, that currently doesn't provoke any reaction.
Ah—an air horn! Great suggestion.
(Actually, it's not that great. An air horn is hardly a benign sound. But because air horns are inherently funny, let's pretend that Sutton is largely unaffected by them at this point.)

Other examples of neutral stimuli include teddy bears, bananas, and the sound of your boss' voice before they became your boss. With classical conditioning, these innocent sights and sounds can all become terrifying fear triggers.
Step 2. The Acquisition Phase
Now let's poke Sutton in the eye and simultaneously blast him with the air horn.

This is called the acquisition phase of classical conditioning. It involves pairing our unconditioned stimulus (a sharp pencil) and our neutral stimulus (an air horn).

A single painful experience may be enough to condition Sutton. But let's repeat the acquisition process for good measure. After all, good science means getting hard results.

After some repetition, Sutton forms a powerful association in his mind. We can lose the pencil altogether now. The sound of the air horn alone causes him to anticipate acute physical pain.
Classical conditioning works by leveraging unconscious pattern-finding instincts. We've now created a pattern of association that triggers the fight-or-flight response.
For our eager volunteer, this manifests in a spike in heart rate and blood pressure, as well as a solid shot of cortisol.
In technical terms, the air horn has become a conditioned stimulus (CS). And it produces a conditioned response (CR).

Step 3. The Generalisation Phase
Now Sutton can't go to sports events anymore. He also flinches at my approach, making him look quite silly to a casual onlooker.
But an even more curious thing happens next. Generalisation means that any horn-like sound now triggers anxiety in Sutton.
Even the mere sight of an air horn, or the mention that I have one in my pocket, now makes Sutton distressed.
Sutton is now so wary of air horns that he's unconsciously on the lookout for any horn-like sights or sounds. Bless him! He thinks this will keep him safe.
Step 4. The Extinction Phase
Now, because Sutton's actually quite smart, over time he'll learn that air horns don't really produce stabbing pains in the eye.
He realises his conditioned fear response is unwarranted, and the unconscious association enters the extinction phase.
Sutton once again has a normal reaction to air horns.

If we do nothing more, the conditioned response will fade away altogether. Which would be a terrible shame for our experiment.
Fortunately, the extinction can be reversed. We can reinforce the association with an unholy horn blast and a solid poke in the eye. Right when he least expects it.

The link between conditioned stimulus and response is restored—and so much faster than the first time! Sutton is inappropriately afraid of air horns once more.
This is the power of classical conditioning. Try it today on a friend near you. For science!

PS. Sutton please don't come after me with an air horn.

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